The purpose of this study is to identify aspects of humoral immunity to HIV which impart protection against infection. This goal will be accomplished by producing and characterizing human monoclonal antibodies (mAbs) to HIV and will culminate in the identification of mAbs for administration to pregnant, HIV-infected women to block maternal-fetal transmission. Other goals include the definition of correlates of humoral immunity that protect infants from infection and the identification of epitopes to be incorporated into vaccines to generate protective Abs against HIV. To accomplish these aims, the proposed work will focus on the following: (a) To produce human mAbs against a variety of HIV epitopes using techniques developed over the past six years in their laboratory for the production of stable lymphoblastoid lines and heterohybridomas secreting anti-HIV mAbs. These mAbs will be selected on the basis of their specificity to several regions of HIV, i.e., the flanking regions of the V3 loop of gp120, the CD4 binding domain of gp120, the fusion domain of gp41 and putative neutralizing epitopes of p17. (b) To define the immunochemical characteristics of each mAb: The isotype and binding affinity of each mAb for its relevant peptide and recombinant protein will be determined. The linear or conformational dependence of the epitopes will be identified as well as the specific amino acids of the binding site of the antigen. Cross-reactivity with peptides of various viral strains will determine type and group- specificity of each mAb. (c) To analyze the biological function of each category of mAb: Each mAb will be assayed for its ability to mediate Ab-dependent cellular cytotocicity, Ab-dependent enhancement of HIV infectivity, complement-mediated virolysis and neutralization of laboratory and primary isolates of the virus. Mixtures of two or more mAbs and mixtures of given mAb and patients' sera will be assayed for synergistic, antagonistic or additive properties. (d) To measure the levels of protective Abs in the sera of infected mothers: Using panels of banked sera form epidemiologic studies and the mAbs generated as part of this project, the specificity, affinity, isotype, quantity and function of protective polyclonal serum Abs will be studied. The levels of these Abs will be compared in the sera of infected pregnant women who bear infected or uninfected infants to identify which, if any, correlate with prevention of transmission.